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21.
The interaction of two groups of murine genes determines the persistence of Theiler''s virus in the central nervous system. 下载免费PDF全文
J F Bureau X Montagutelli S Lefebvre J L Gunet M Pla M Brahic 《Journal of virology》1992,66(8):4698-4704
Theiler's murine encephalomyelitis virus is responsible for a chronic inflammatory demyelinating disease of the central nervous system of the mouse. The disease is associated with persistent viral infection of the spinal cord. Some strains of mice are susceptible to viral infection, and other strains are resistant. The effect of the genetic background of the host on viral persistence has not been thoroughly investigated. We studied the amount of viral RNA in the spinal cords of 17 inbred strains of mice and their F1 crosses with the SJL/J strain and observed a large degree of variability among strains. The pattern of viral persistence among mouse strains could be explained by the interaction of two loci. One locus is localized in the H-2D region of the major histocompatibility complex, whereas the other locus is outside this complex and is not linked to the Tcrb locus on chromosome 6. 相似文献
22.
本文报道了寄生在云杉上的中国新记录种顶裂盘菌(Lophophacidium hyperboreumLagerb.);首次发现了这个种的无性型座壳梭孢属(Apostrasseria sp.),证实了融雪前病株针叶上有表生的菌丝和小菌核;查清了它是新疆云杉林中的广布种,引致云杉雪枯病;发现了新分布区,地理分布范围在75°—94°E,37°40′—49°N;发现了新寄主,多土的西伯利亚云杉(Picea obovata Ledeb.)和引进的青海云杉(P.crassifolia Kom.)、川西云杉(P.balfourianaRehd.et Wils.)。 相似文献
23.
Céline Arzel Johan Elmberg Matthieu Guillemain Michel Lepley Fabrice Bosca Pierre Legagneux Jean-Baptiste Nogues 《Journal of Ornithology》2009,150(1):61-73
Two frequent assumptions about the evolution of long-distance migration in birds are that they travel long distances annually
to reach food-rich areas for breeding, and that they time their migratory journey to be at staging sites when the latter provide
the best feeding conditions. These assumptions have rarely been properly tested, and there is no study in which a species’
major food types have been measured by standardized methods throughout a flyway and over a large part of the year. We here
present such data for Eurasian teal (Anas crecca), converted to a common energetic currency, and collected at wintering, spring staging and breeding sites. Teal did not time
migration to maximize local food abundance; most birds left wintering and spring staging sites before a sharp increase in
invertebrate food abundance occurred. On the other hand, hatching of ducklings coincided with a peak in invertebrate food
abundance on boreal breeding lakes. Mean overall food abundance (invertebrates and seeds combined) did not differ between
wintering sites in southern France and breeding sites in northern Sweden at the time of breeding. Our results are inconsistent
with the hypothesis that long-distance migration in dabbling ducks has evolved because adult birds gain an immediate pay-off
in increased food abundance by flying north in spring. However, our data confirm a selective advantage for breeding at higher
latitudes, because hatching of ducklings may coincide with a peak in invertebrate emergence and because longer days may increase
the duration of efficient foraging. 相似文献
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Fabrice Helfenstein Tibor Szép Zsolt Nagy Bart Kempenaers Richard H. Wagner 《Journal of avian biology》2008,39(6):647-652
Sperm mobility is known to be an important determinant of a male's sperm competitive ability. Although more debated, sperm length and its relation to sperm swimming ability has also been proposed to determine a male's fertilisation potential. Furthermore, both mobility and length may covary with a male's phenotype, either positively (the phenotype‐linked fertility hypothesis) or negatively if, for instance, low‐quality males have less access to females but invest more in sperm production. Using dummy females, we collected sperm samples from wild sand martins Riparia raparia males. We investigated the relationship between sperm length and sperm swimming speed as measured by sperm straight line velocity (VSL), and determined whether sperm traits are correlated with male body size and condition. We found that total sperm length is repeatable within‐ejaculate and shows substantial inter‐male variation. Sperm length was associated with sperm velocity: males with short sperm have sperm that swim initially faster but die sooner, whereas males with longer sperm have sperm that swim more slowly but for a longer time. Smaller males produced sperm with higher overall velocity. This correlation between male size and sperm behaviour may reflect alternative fertilisation strategies where small males having less mating opportunities invest more in sperm competitive ability. The existence of such alternative strategies would participate in maintaining variation in sperm length and velocity in this species. 相似文献
28.
The influence of anionic lipids on SHIP2 phosphatidylinositol 3,4,5-trisphosphate 5-phosphatase activity 总被引:1,自引:0,他引:1
The SH2 domain containing inositol 5-phosphatase 2 (SHIP2) catalyzes the dephosphorylation of phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) to phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2) and participates in the insulin signalling pathway in vivo. In a comparative study of SHIP2 and the phosphatase and tensin homologue deleted on chromosome 10 (PTEN), we found that their lipid phosphatase activity was influenced by the presence of vesicles of phosphatidylserine (PtdSer). SHIP2 PtdIns(3,4,5)P3 5-phosphatase activity was greatly stimulated in the presence of vesicles of PtdSer. This effect appears to be specific for di-C8 and di-C16 fatty acids of PtdIns(3,4,5)P3 as substrate. It was not observed with inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) another in vitro substrate of SHIP2, nor with Type I Ins(1,4,5)P3/Ins(1,3,4,5)P4 5-phosphatase activity, an enzyme which acts on soluble inositol phosphates. Vesicles of phosphatidylcholine (PtdCho) stimulated only twofold PtdIns(3,4,5)P3 5-phosphatase activity of SHIP2. Both a minimal catalytic construct and the full length SHIP2 were sensitive to the stimulation by PtdSer. In contrast, PtdIns(3,4,5)P3 5-phosphatase activity of the Skeletal muscle and Kidney enriched Inositol Phosphatase (SKIP), another member of the mammaliam Type II phosphoinositide 5-phosphatases, was not sensitive to PtdSer. Our enzymatic data establish a specificity in the control of SHIP2 lipid phosphatase activity with PtdIns(3,4,5)P3 as substrate which is depending on the fatty acid composition of the substrate. 相似文献
29.
松辽盆地白垩纪微体浮游植物群及其环境讨论 总被引:7,自引:2,他引:7
该文报道了松辽盆地白垩纪丰富的非海相微体浮游植物群,主要是沟鞭藻类及一些绿藻和疑源类;论述了藻类的生物地层特征,自下而上初步划分出10个组合带;结合微量元素和古地磁等资料,较详细地讨论了含微体浮游植物组段的沉积环境,认为松辽盆地在白垩纪至少遭受过两次重要的海侵(分别在青山口组一段及嫩江组一、二段沉积时期),导致古松辽湖泊五种不同水体环境的演替,指出微体浮游植物组合的变化是受古盐度、古温度和古水深等因素控制的。此外,对有关组段的地质时代也进行了讨论,进一步补充了新的浮游植物化石证据。 相似文献
30.
J Bureau J Hubert M Bouteille 《Biology of the cell / under the auspices of the European Cell Biology Organization》1986,56(1):7-16
Co-isolated residual nuclear shells and residual nucleoli from membrane-depleted rat liver nuclei were spread according to Kleinschmidt's method. Comparison of the spread residual structures isolated from nuclear shells and spread pore complex-lamina isolated from nuclear envelopes showed that these residual structures are morphologically identical. Furthermore, our nuclear shell isolation procedure allowed visualization of DNA strands bound to a granular component of the lamina. The fragmentation of nuclear shells allowed us to obtain well-spread nucleolar remnants, in which we observed DNA strands anchored on a residual nucleolar network attached to the lamina. The different molecular features revealed by the spreading of residual nucleolar structures suggest that both non-transcribing nucleolar DNA and active ribosomal genes are linked to the nucleolar network. Although the exact nature of this network remains to be defined, the results of the present study strongly suggest that the DNA molecules of the chromosomes bearing ribosomal genes have many sites of attachment to a non-chromatin nucleolar network which can be referred to as a nucleolar skeletal complex. 相似文献